Linear electric compressor and refrigerant circuit

ABSTRACT

A refrigerant circuit includes a linear electric compressor including a housing with a cylinder bore, a pair of end plates, a valve unit, a piston, an urging device for urging the piston, a coil generating electromagnetic force and a permanent magnet. The permanent magnet cooperates with the urging device and the coil to reciprocate the piston in the cylinder bore. The piston further includes a piston rod and the urging device is provided around the piston rod and a pair of piston heads integrally formed at opposite ends of the piston rod. The diameter of the piston rod is smaller than that of the piston head. The permanent magnet is provided on the piston head and the coil surrounds the piston head. The housing further includes a seat located between the pair of piston heads and the urging device is provided between the seat and each of the piston head.

BACKGROUND OF THE INVENTION

The present invention relates to a linear electric compressor and alsoto a refrigerant circuit including the linear electric compressor.

Japanese Patent No. 3953735 discloses a linear electric compressor whichincludes a double-headed piston including a piston rod and piston headsat the opposite ends of the piston rod and compression chambers formedat the outer end of each piston head. The linear electric compressorfurther includes permanent magnets provided at positions correspondingto the center of the piston rod of the double-headed piston and to eachpiston head thereof and coils provided around the piston rod and eachpiston head. The linear electric compressor still further includes apair of springs provided inside the double-headed piston.

By supplying electric power periodically to energize the coils of thelinear electric compressor of the above patent, periodically variableelectromagnetic force is generated around the coils and the permanentmagnets of the pistons are attracted toward or repelled from the coilsby the electromagnetic force. Accordingly, the pistons reciprocate incylinder bores. The pistons reciprocate also by resonance of naturalfrequency of the springs. The reciprocating movement of the pistonscauses refrigerant gas to be introduced from a suction chamber to acompression chamber, compressed in the compression chamber anddischarged into a discharge chamber. Thus, the linear electriccompressor can be electrically controlled to compress refrigerant gasand used for an air conditioner for an electric vehicle and the like.

Furthermore, this type of linear electric compressor can compressrefrigerant gas twice by a single reciprocating movement of the pistonand, therefore, the performance of compressing refrigerant gas per unittime can be improved and the compressor be made small as compared with alinear electric compressor having a compression chamber only at one endof the piston.

However, the linear electric compressor of the above patent requires aspace in the piston for installing the springs. Therefore, the outerdiameter of the piston is increased and the inner diameter of thecylinder bore needs to be designed accordingly. This type of linearelectric compressor has limitations on downsizing.

The present invention is directed to providing a linear electriccompressor that can be made small while ensuring the performance ofcompressing refrigerant gas per unit time and also a refrigerant circuithaving the linear electric compressor.

SUMMARY OF THE INVENTION

A refrigerant circuit includes a linear electric compressor including ahousing with a cylinder bore, a pair of end plates, a valve unit, apiston, an urging device for urging the piston, a coil generatingelectromagnetic force and a permanent magnet. The permanent magnetcooperates with the urging device and the coil to reciprocate the pistonin the cylinder bore. The piston further includes a piston rod and theurging device is provided around the piston rod and a pair of pistonheads integrally formed at opposite ends of the piston rod. The diameterof the piston rod is smaller than that of the piston head. The permanentmagnet is provided on the piston head and the coil surrounds the pistonhead. The housing further includes a seat located between the pair ofpiston heads and the urging device is provided between the seat and eachof the piston head.

Other aspects and advantages of the invention will become apparent fromthe following description, taken in conjunction with the accompanyingdrawings, illustrating by way of example the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel areset forth with particularity in the appended claims. The inventiontogether with objects and advantages thereof, may best be understood byreference to the following description of the presently preferredembodiments together with the accompanying drawings in which:

FIG. 1 is a cross sectional view of a linear electric compressoraccording to a first embodiment of the present invention;

FIG. 2 is a schematic view of a refrigerant circuit using the linearelectric compressor of FIG. 1;

FIG. 3 is a partially enlarged cross sectional view of the linearelectric compressor of FIG. 1;

FIG. 4 is a schematic view showing coils and permanent magnets of thelinear electric compressor of FIG. 1;

FIG. 5 is a schematic view of a refrigerant circuit according to asecond embodiment of the present invention;

FIG. 6 is an enlarged cross sectional view showing a flow sensor andtubes to which the flow sensor is mounted in the refrigerant circuit ofFIG. 5;

FIG. 7 is a schematic view of a refrigerant circuit according to a thirdembodiment of the present invention; and

FIG. 8 is an enlarged cross sectional view showing the flow sensor andtubes to which the flow sensor is mounted in the refrigerant circuit ofFIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe the linear electric compressor and therefrigerant circuit according to the first through third embodiments ofthe present invention with reference to FIGS. 1 through 8. The linearelectric compressor 100 according to the first embodiment and therefrigerant circuits 140, 200, 300 according to the first through thethird embodiments, respectively, are employed for an air conditioner fora hybrid vehicle or an electric vehicle.

As shown in FIG. 1, the linear electric compressor 100 includes a firstand a second cylinder blocks 1, 3, a shell 5 and a center housing 7,which cooperate to form a housing 9 of the linear electric compressor100. The first and the second cylinder blocks 1, 3 have formed therein afirst and a second cylinder bores 1A, 3A, respectively. The first andthe second cylinder bores 1A, 3A are designed so that they are coaxiallyformed and have the same diameter.

The first and the second cylinder blocks 1, 3 have a first and a secondflanges 1B, 3B around the first and the second cylinder bores 1A, 3A,respectively, which are housed in the shell 5 so that the first and thesecond flanges 1B, 3B are located at the opposite ends of the shell 5.The center housing 7 is provided in the shell 5 between the first andthe second cylinder blocks 1, 3. The center housing 7 has formedtherethrough in axial direction thereof an accommodation hole 7A whichis coaxial with the first and the second cylinder bores 1A, 3A and thediameter of which is substantially the same as those of the first andthe second cylinder bores 1A, 3A.

A first and a second end plates 11, 13 are joined to the opposite endsof the shell 5 through a first and a second gaskets 10, 12,respectively. The first and the second end plates 11, 13 have formedtherein recesses, respectively and a first and a second valve plates 15,17 are held between the first gasket 10 and the first end plate 11 andbetween the second gasket 12 and the second end plate 13, respectively.A first and a second discharge chambers 11A, 13A are formed by therecesses between the first and the second end plates 11, 13 and thefirst and the second valve plates 15, 17, respectively. The first andthe second end plates 11, 13 have formed therethrough a first and asecond discharge ports 11B, 13B, respectively. The first and the seconddischarge chambers 11A, 13A are connected to tubes 101, 102 shown inFIG. 2 through the first and the second discharge ports 11B, 13B,respectively. The first and the second discharge chambers 11A, 13A formthe discharge chamber of the present invention.

As shown in FIG. 3, the first valve plate 15 has formed therethrough adischarge port 15A. A reed type discharge valve 19 for opening andclosing the discharge port 15A and a retainer 21 for regulating theopening of the discharge valve 19 are fixed by a rivet 23 to the firstvalve plate 15 on the first discharge port 11B side. The first valveplate 15, the discharge valve 19, the retainer 21 and the rivet 23cooperate to form a first valve unit 25. Similarly, a second valve unitis formed on the second valve plate 17 side. The first and the secondvalve units 25 are provided between the first and the second cylinderbores 1A, 3A and the first and the second end plates 11, 13,respectively.

As shown in FIG. 1, the first and the second cylinder bores 1A, 3A andthe accommodation hole 7A receive therein a reciprocally slidable piston27. The piston 27 includes a piston rod 29 and a first and a secondpiston heads 31, 33 which are integrally provided with the piston rod 29at the opposite ends of the piston rod 29, respectively and slidable inthe first and the second cylinder bores 1A, 3A, respectively.

As shown in FIGS. 3 and 4, the first piston head 31 includes a head 39,on outer surface of which permanent magnets 35, 37 are fixed, and afirst and a second spacers 41, 43 which are integrally provided with thehead 39 and form a space between the inner surface of the first cylinderbore 1A and the outer surface of the permanent magnets 35, 37.

The permanent magnets 35, 37 are ring shaped and use a rare-earthmagnet. North and south poles of the permanent magnet 35 are located onthe outer surface thereof and the inner surface thereof, respectively,and, on the other hand, south and north poles of the permanent magnet 37are located on the outer surface thereof and the inner surface thereof,respectively. The polar character of the permanent magnets 35, 37 may bereversed.

In installing the permanent magnets 37, 35, firstly the second spacer 43is press-fit on the head 39, the permanent magnets 37, 35 are press-fiton the outer surface of the head 39, and then the first spacer 41 ispress-fit on the outer surface of the head 39, as shown in FIG. 3. Thus,the permanent magnets 35, 37 are held securely on the outer surface ofthe head 39 between the first and the second spacers 41, 43. Acompression chamber 45 is formed in the first cylinder bore 1A by thespace outward of the first spacer 41 of the first piston head 31.

As shown in FIG. 3, a suction port 39A is formed through the head 39 forfluid communication between the inside of the head 39 and thecompression chamber 45. The first spacer 41 has formed therethrough avalve hole 41A that is communicable with the suction port 39A, andhouses therein a float-type suction valve 47. The valve hole 41A has astop 41B formed on the side thereof adjacent to the compression chamber45. The suction valve 47 is formed in the outer periphery thereof with aplurality of engagement plates 47A that are brought into contact withthe stop 41B when the suction port 39A is opened. A cutout 47B is formedbetween any two adjacent engagement plates 47A.

As shown in FIG. 1, the first and the second piston heads 31, 33 arepress-fit on the opposite ends of the piston rod 29. The diameter of thepiston rod 29 is smaller than those of the first and the second pistonheads 31, 33. The piston rod 29 has formed therethrough in axialdirection thereof a suction passage 29A. The suction passage 29Aincludes also radially extending passages in the center of the pistonrod 29 so as to open at the outer peripheral surface of the piston rod29. As shown in FIG. 3, the suction passage 29A communicates with thesuction port 39A of the first piston head 31. The suction passage 29A,the suction port 39A, the suction valve 47 and the first spacer 41cooperate to form a suction valve unit 50. The suction valve unit on thesecond piston head 33 side has substantially the same structure.

As shown in FIG. 1, the center housing 7 has formed on the innerperipheral surface and at the center thereof a seat 7B that protrudesinto the accommodation hole 7A at the center between the opposite outerend surfaces of the first and the second cylinder blocks 1, 3. It can bealso said that the seat 7B is located between the first and the secondpiston heads 31, 33. The space between the inner peripheral surface ofthe accommodation hole 7A and the outer peripheral surface of the pistonrod 29 forms a spring chamber 7C communicating with the suction passage29A. The spring chamber 7C houses therein a first and a second coilsprings 49, 51 as an urging device for urging the piston 27.

The first coil spring 49 is preloaded with one end thereof in contactwith the seat 7B and the other end thereof in contact with the secondspacer 43 of the first piston head 31.

The center housing 7 and the shell 5 forms therebetween an intermediatechamber 53. The intermediate chamber 53 may be provided in either thecenter housing 7 or the shell 5. A communication hole 7D that connectsthe intermediate chamber 53 and the spring chamber 7C is formed in thecenter housing 7. The intermediate chamber 53 is communicable with thefirst and the second cylinder bores 1A, 3A through the suction passage29A. Combination of the intermediate chamber 53 and the spring chamber7C forms a suction chamber 55. An inlet 5A is formed through the shell5. The suction chamber 55 is connected to a tube 103 shown in FIG. 2through the inlet 5A. A cover 57 is fixed to the shell 5 for closing theintermediate chamber 53. Terminals (not shown) that are connected tocoils 63A, 63B, 65A, 65B as will be described hereinafter are fixed tothe cover 57.

The coils 63A, 63B and 65A, 65B are provided between the shell 5 and thefirst and the second cylinder blocks 1, 3, with the coils 63A, 63B and65A, 65B held by a first and a second support members 59, 61,respectively. The coils 63A, 63B and 65A, 65B are disposed so as tosurround the first and the second piston heads 31, 33, respectively. Thefirst and the second cylinder blocks 1, 3 and the first and the secondsupport members 59, 61 are made of a magnetic material. Alternatively,the first and the second cylinder blocks 1, 3 may be made of anonmagnetic material

As shown in FIG. 2, the tubes 101, 102 connect the linear electriccompressor 100 to a tube 104, which is in turn connected to a condenser105. The condenser 105 is connected to an expansion valve 107 and anevaporator 108 through a tube 106. The evaporator 108 is connected to atube 103. The terminals in the intermediate chamber 53 for the coils63A, 63B, 65A, 65B are connected to a power supply 110 through a leadwire 109. The power supply 110 is electrically controlled. The abovecomponents cooperate to form the refrigerant circuit 140.

The power supply 110 supplies electric power to energize the coils 63A,63B, 65A, 65B of the linear electric compressor 100 periodically therebyto generate periodically variable electromagnetic force around the coils63A, 63B, 65A, 65B. Referring to FIG. 4, when the coil 63A attracts thepermanent magnet 35 of the first piston head 31, magnetic repulsion isgenerated between the coil 63B and the permanent magnet 37 of the firstpiston head 31. On the other hand, when magnetic repulsion is generatedbetween the coil 63A and the permanent magnet 35 of the first pistonhead 31, the coil 63B attracts the permanent magnet 37 of the firstpiston head 31. Thus, the piston 27 is caused to reciprocate in thefirst and the second cylinder bores 1A, 3A. The piston 27 alsoreciprocates by resonance due to natural frequencies of the first andthe second coil springs 49, 51.

Strokes of suction, compression and discharge of refrigerant gas areaccomplished by the reciprocating movement of the piston 27. Thefollowing will describe the operation of the linear electric compressor.The description will focus on the movement of the first piston head 31.As shown in FIG. 3, when the first piston head 31 is in the suctionstroke, the pressure in the compression chamber 45 is reduced and,accordingly, the suction valve 47 moves within the valve hole 41A so asto open the suction port 39A. Therefore, refrigerant gas in the suctionchamber 55 flows from the suction port 39A into the compression chamber45 through clearances between the cutouts 47B of the suction valve 47and the stop 41B. Then, the discharge port 15A is closed by thedischarge valve 19.

When the first piston head 31 begins its compression stroke, the suctionvalve 47 moves within the valve hole 41A so as to close the suction port39A. Accordingly, the pressure in the compression chamber 45 isincreased thereby to open the discharge valve 19. Thus, the first pistonhead 31 begins its discharge stroke and the compressed refrigerant gasis discharged into the first discharge chamber 11A through the dischargeport 15A. Though the refrigerant gas in the first discharge chamber 11Ais hot, the first gasket 10 provided between the first end plate 11 andthe first cylinder block 1 prevents the piston 27 from being exposeddirectly to the first discharge chamber 11A. Therefore, the piston 27 isunsusceptible to the heat of the refrigerant gas in the first dischargechamber 11A. The same is true of the second piston head 33 side when thesecond piston head 33 is in the compression stroke.

Referring to FIG. 2, refrigerant gas flowing out from the evaporator 108through the tube 103 flows into the compression chamber 45 through thesuction chamber 55. Refrigerant gas is compressed in the compressionchamber 45 and then discharged into the first and the second dischargechambers 11A, 13A. Refrigerant gas in the first and the second dischargechambers 11A, 13A flows out therefrom through the tubes 101, 102 to thecondenser 105, the expansion valve 107 and the evaporator 108. Thelinear electric compressor 100 which is operable to compress refrigerantgas by electrical control may be used advantageously for airconditioning for an electric vehicle and the like. For example, when theengine of a hybrid vehicle is turned off while the hybrid vehicle is ata stop, comfortable air conditioning can be achieved by the electricallycontrolled linear electric compressor 100.

The linear electric compressor 100 of the present embodiment cancompress refrigerant gas twice by a single reciprocating movement of thepiston 27, thus improving the performance of compressing refrigerant gasper unit time as compared with a linear electric compressor having acompression chamber only at one end of a piston rod.

Furthermore, the linear electric compressor 100 includes the first andthe second coil springs 49, 51 in the center of the double-headed piston27. The diameter of the piston rod 29 is smaller than that of the firstand the second piston heads 31, 33. The first and the second coilsprings 49, 51 are provided in the spring chamber 7C, the diameter ofwhich is substantially the same as that of the first and the secondcylinder bores 1A, 3A. Therefore, the linear electric compressor 100dispenses with an urging device in the compression chamber 45 and thecompression chamber 45 can be made large. Since the diameter of thefirst and the second coil springs 49, 51 is not larger than that of thefirst and the second piston heads 31, 33, the inner diameter of thefirst and the second cylinder bores 1A, 3A and the accommodation hole 7Aof the center housing 7 can be designed in accordance with the outerdiameter of the first and the second piston heads 31, 33.

Therefore, the linear electric compressor 100 can be made smaller whileachieving high performance of compressing refrigerant gas per unit time.The refrigerant circuit 140 employing the linear electric compressor 100can be also made small while maintaining high compression performance.

In the linear electric compressor 100 of the present embodiment whereinthe permanent magnets 35, 37 are provided in the first and the secondpiston heads 31, 33 and the coils 63A, 63B and 65A, 65B are providedaround the first and the second piston heads 31, 33, respectively, theelectromagnetic force and the permanent magnets 35, 37 operate eachother at the opposite ends of the double-headed piston 27. Therefore, itis hard for the ends of the piston 27 to deflect in radial direction ofthe piston 27, which makes it difficult for the first and the secondpiston heads 31, 33 to interfere with the inner surface of the first andthe second cylinder bores 1A, 3A, respectively.

Since the housing 9 of the linear electric compressor 100 includes thefirst and the second cylinder blocks 1, 3 and the shell 5, it is easy toinstall the coils 63A, 63B and 65A, 65B between the shell 5 and therespective first and the second cylinder blocks 1, 3, thus facilitatingmanufacturing of the linear electric compressor 100.

The intermediate chamber 53 of the linear electric compressor 100 isformed by the shell 5 and the center housing 7 between the first and thesecond cylinder blocks 1, 3. The first and the second discharge chambers11A, 13A are formed in the first and the second end plates 11, 13 byproviding the valve units 25, respectively, and the suction valve units50 are provided in the first and the second piston heads 31, 33,respectively. Moreover, the spring chamber 7C and the suction passage29A both serving also as a part of the suction chamber 55 are formed inthe piston 27. This structure makes it possible for the linear electriccompressor 100 to be made small and light while achieving highperformance of compressing refrigerant gas.

Now referring to FIG. 5, the refrigerant circuit 200 according to thesecond embodiment is made by modifying a part of the refrigerant circuit140 (FIG. 2) according to the first embodiment. As shown in FIG. 5, thetube 104 of the first embodiment is replaced by a tube 150. The tube 150is provided between the condenser 105 and the respective first and thesecond discharge chambers 11A, 13A (FIG. 1). The refrigerant circuit 200includes a flow sensor 111 as a detecting device and a control device112.

As shown in FIG. 6, a throttle 70 is provided inside the tube 150.Reference symbols 150A and 150B designate first and second positions inthe refrigerant circuit 200 that are upstream and downstream of thethrottle 70, respectively, with respect to the flowing direction ofrefrigerant gas in the tube 150 indicated by arrow. An upstream tube 120is connected to the first position 150A and a downstream tube 121 isconnected to the second position 150B, respectively.

The flow sensor 111 is provided in the tube 150 for detecting a pressuredifference between the first pressure P1 and the second pressure P2 ofrefrigerant gas flowing through the first position 150A and the secondposition 150B, respectively. The flow sensor 111 includes a sensor body71 and a hall device 73 as a magnetic force detecting device.

The sensor body 71 houses a spool 75 that is movable in verticaldirection. A moving permanent magnet 77 is fixed to the spool 75. Aspring seat 79 is fixed to lower end of the sensor body 71 and a firstspring 81 is provided between the spring seat 79 and the spool 75 forurging the spool 75 upward as viewed in the drawing. A second spring 83is provided between upper inner surface of the sensor body 71 and thespool 75 for urging the spool 75 downward.

The upstream tube 120 is connected to the sensor body 71 at a positionthat is higher than that of the spool 75 and the downstream tube 121 isconnected to the spring seat 79, as shown in FIG. 6. When the secondpressure P2 is higher than the first pressure P1, the spool 75 is movedupward against the urging force of the second spring 83 in the sensorbody 71. When the second pressure P2 is lower than the first pressureP1, on the other hand, the spool 75 is moved downward against the urgingforce of the first spring 81 in the sensor body 71.

The hail device 73 is fixed to top surface of the sensor body 71. Thehall device 73 detects the magnetic flux density that is variable inaccordance with the vertical movement of the spool 75 with the movingpermanent magnet 77 toward and away from the hall device 73. As shown inFIG. 5, the hall device 73 is electrically connected to the controldevice 112 through a first control circuit 130. The hall device 73generates to the control device 112 a control signal representing thedetected magnetic flux density.

The control device 112 includes a stroke computing part 113 and avoltage-frequency controlling part 114. The control device 112 iselectrically connected to the power supply 110 through a second controlcircuit 131.

The stroke computing part 113 of the control device 112 computes thepresent position of the piston 27 (FIG. 1) based on the control signalreceived from the hall device 73, i.e., the flow rate of refrigerant gasflowing through the tube 150. The position of the piston 27 representsto the state quantity of the linear electric compressor 100. The statequantity of the linear electric compressor 100 can be a physicalquantity influenced by the current position of the piston 27 asindicated above, a pressure or a temperature of refrigerant gas beingdischarged from the linear electric compressor 100 or flowing thereinto,or a combination of these state quantities. In other words, the physicalquantity can be determined indirectly by measuring the flow rate ofrefrigerant gas flowing through the linear electric compressor 100 orany tube in the refrigerant circuit 200 with the aid of a flow meter. Inthe case of the present embodiment, the physical quantity shouldpreferably be the pressure difference between the first pressure P1 inthe first position 150A and the second pressure P2 in the secondposition 1508 that is located downstream of the first position 150A. Thestroke computing part 113 determines the current position of the piston27 by backward calculation of the drive frequency of the piston 27. Thestroke computing part 113 shown in FIG. 5 generates to thevoltage-frequency controlling part 114 a control signal representing thestate quantity of the linear electric compressor 100.

The voltage-frequency controlling part 114 of the control device 112controls the voltage, the current and the current frequency of electricpower supplied from the power supply 110 to the linear electriccompressor 100, based on the control signal that is received from thestroke computing part 113. The voltage-frequency controlling part 114can control independently the voltage, the current and the currentfrequency of electric power which is supplied from the power supply 110to the linear electric compressor 100, i.e., the voltage, the currentand the cycle length of current of electric power which is supplied tocoils 63A, 63B, 65A, 65B. The same reference numerals are used for thecommon elements or components of the refrigerant circuit 200 and therefrigerant circuit 140 according to the first embodiment, and thedescription of such elements or components for the second embodimentwill be omitted.

The power supply 110 in the refrigerant circuit 200 according to thesecond embodiment supplies electric power to the linear electriccompressor 100 based on the state quantity. The state quantity of thelinear electric compressor 100 in the refrigerant circuit 200 isdetermined by detecting the physical quantity influenced by the positionof the piston 27 (FIG. 1) in the linear electric compressor 100. Thus,the electric power supplied to the linear electric compressor 100 iscontrolled based on the state quantity. Not only when the voltage andthe current which are supplied to the coils 63A, 63B, 65A, 65B,respectively increase but also when the periodic voltage and current arekept constant, the thermal load and the pressure of refrigerant gas inthe compression chamber 45 of the linear electric compressor 100changes. Then, the distance of reciprocating movement of the piston 27,i.e., the piston stroke, caused by the electromagnetic force generatedby the predetermined electric power also changes. For example, when thethermal load is low and the pressure of refrigerant gas in thecompression chamber 45 decreases, the first and the second pistons maycollide against their corresponding valve units and the collision causesnoise and vibration in the linear electric compressor 100. This maydecrease the durability of the linear electric compressor 100.Therefore, when the thermal load decreases and the pressure of therefrigerant gas in the compression chamber 45 of the linear electriccompressor 100 also decreases, the collision of the first and the secondpiston heads 31, 33 against the first and the second valve plates 15,17, respectively, can be prevented by the refrigerant circuit 200according to the second embodiment having the above-mentioned controlbased on the state quantity. Accordingly, the durability of the linearelectric compressor 100 in the refrigerant circuit 200 can be alsoimproved.

The flow sensor 111 in the refrigerant circuit 200 can detects thepressure difference between the first pressure P1 and the secondpressure P2 in the tube 150 by detecting the change of the magnetic fluxdensity. Therefore, the flow rate of refrigerant gas flowing through thetube 150 can be detected precisely at a moderate cost. The flow sensor111 which is provided in the tube 150 away from the linear electriccompressor 100 is free from the influence of the magnetic flux generatedby the coils 63A, 63B, 65A, 65B of the linear electric compressor 100.

In the refrigerant circuit 200 according to the second embodiment, thethrottle 70 is provided in the tube 150 in which high-pressurerefrigerant gas flows. Therefore, pressure loss of refrigerant gasincurred in the throttle 70 does not decrease the performance of therefrigerant circuit 200. The other advantageous effects are the same asthose in the refrigerant circuit according to the first embodiment.

Referring to FIG. 7, the refrigerant circuit 300 according to the thirdembodiment differs from the refrigerant circuit 200 of the secondembodiment in that the flow sensor 111 is provided in a bend 90 of thetube 103. Accordingly, in the refrigerant circuit 300 of the thirdembodiment, the tube 104 that is used in the refrigerant circuit 140 ofthe first embodiment is used in place of the tube 150 in the refrigerantcircuit 200 of the second embodiment. No throttle such as 70 is providedin the refrigerant circuit 300.

Referring to FIG. 8, reference symbols 130A, 130B designate first andsecond positions in the tube 103 of the refrigerant circuit 300 that areupstream and downstream of the bend 90, respectively, with respect tothe flowing direction of refrigerant gas in the tube 103 indicated bybent arrow. The upstream tube 120 is connected to the first position103A and the downstream tube 121 is connected to the second position1038. The same reference numerals are used for the common elements orcomponents of the refrigerant circuits 200 and 300 according to thesecond and the third embodiments, and the description of such elementsor components for the third embodiment will be omitted.

The flow sensor 111 in the refrigerant circuit 300 can detect thepressure difference between the first pressure P1 and the secondpressure P2 of refrigerant gas flowing through the first position 103Aand the second position 103B, respectively, based on the flow passageresistance caused by the bend 90 through which refrigerant gas flows. Byinstalling the flow sensor 111 to the bend 90 of the tube 103 which isinevitably formed for mounting of the refrigerant circuit 300 to thevehicle, the flow rate of refrigerant gas flowing through the tube 103is detected easily and efficiently. The bend 90 may not necessarily beformed by bending the tube 103 at almost a right angle. As long as aresistance is generated against the refrigerant gas flowing through thebend 90, the bend 90 may be formed by bending the tube 103 at any angleother than a right angle. Additionally, the bend 90 may be provided at aposition in which high-pressure refrigerant gas flows, e.g., at aposition anywhere in the tube 104. The other advantageous effects arethe same as those in the refrigerant circuit 200 according to the secondembodiment.

The present invention is not limited to the first through thirdembodiments, but may be modified within the effects of the presentinvention.

The linear electric compressor 100 according to the first embodiment isused alone, but it may be used in combination with any other compressor.This is also applicable to the second and the third embodiments.

In the first through third embodiments, the first and the seconddischarge chambers 11A, 13A are formed on the first and the second endplate 11, 13 sides, respectively and a suction chamber 55 is formed inthe piston 27. However, suction chambers may be formed on the first andthe second end plate 11, 13 sides, respectively and a discharge chambermay be formed in the piston 27.

The first and the second spacers 41, 43 may be made of fluororesin suchas PTFE. In this case, the piston 27 reciprocates suitably in the firstand the second cylinder bores 1A, 3A.

The suction valve unit 50 may be of a reed type.

As the detecting device for detecting the piston 27, any suitable sensormay be used, including a position sensor using laser or magnetic flux, adifferential transformer and a proximity switch.

A plurality of flow sensors 111 may be provided in the tubes 101-104(150), 106. For detecting the state of refrigerant gas flowing throughthe linear electric compressor 100 and the tubes 101-104 (105), 106 withan increased accuracy, a pressure sensor and a temperature sensor may beused in place of the flow sensor 111. In this case, the stroke computingpart 113 can compute the physical quantity more accurately.

The refrigerant circuit according to the present invention may be usedfor a hybrid vehicle and an electric vehicle using an electric motor. Itis also applicable to a vehicle equipped with an engine.

1. A linear electric compressor comprising: a housing having formedtherein a cylinder bore; a pair of end plates joined to opposite ends ofthe housing; a valve unit provided between the cylinder bore and the endplate, wherein a compression chamber is located on the cylinder boreside of the valve unit and a discharge chamber or a suction chamber islocated on the end plate side of the valve unit; a pistonreciprocally-slidably received in the cylinder bore, wherein the pistonand the valve unit cooperate to form the compression chamber in thecylinder bore; an urging device for urging the piston in the directionfor the piston to reciprocate; a coil provided in the housing andgenerating electromagnetic force; and a permanent magnet provided in thepiston, the permanent magnet cooperate with the urging device and thecoil to reciprocate the piston in the cylinder bore, wherein the pistonincludes: a piston rod; and a pair of piston heads integrally formed atopposite ends of the piston rod, the piston heads are slidable in thecylinder bore, wherein the diameter of the piston rod is smaller thanthat of the piston head, wherein the permanent magnet is provided on thepiston head and the coil surrounds the piston head; wherein the housingincludes: a seat located between the pair of piston heads, wherein theurging device is provided around the piston rod between the seat andeach of the piston head.
 2. The linear electric compressor according toclaim 1, wherein the housing includes: a cylinder block having formedtherein the cylinder bore; and a shell housing the cylinder block,wherein the coil is provided between the shell and the cylinder block.3. The linear electric compressor according to claim 2, wherein thepiston has a suction passage provided between the pair of piston heads,the linear electric compressor further comprising: an intermediatechamber provided in any one of the cylinder block and the shell, orbetween the cylinder block and the shell, the intermediate chambercommunicates with the suction passage, wherein the discharge chamber islocated on the end plate side of the valve unit; wherein the piston headincludes a suction valve unit between the compression chamber and thesuction passage, wherein the intermediate chamber forms the suctionchamber.
 4. The linear electric compressor according to claim 1, whereinthe housing further comprises an accommodation hole which is coaxialwith the cylinder bore and has the same diameter as that of the cylinderbore, wherein the urging device is disposed between the cylinder rod andthe accommodation hole.
 5. The linear electric compressor according toclaim 4, wherein the seat protrudes from inner surface of the housinginto the accommodation hole so as to receive the end of the urgingdevice.
 6. A refrigerant circuit comprising: the linear electriccompressor according to; a condenser; an expansion valve; an evaporator;a plurality of tubes connecting above components and through whichrefrigerant gas flows; a power supply supplying electric power to thecoil of the linear electric compressor; a detecting device detecting astate quantity of the linear electric compressor; and a control devicecontrolling the electric power that the power supply supplies, based onthe state of quantity detected by the detecting device.
 7. Therefrigerant circuit according to claim 6, wherein the state of quantityis a physical quantity influenced by a position of the piston of thelinear electric compressor.
 8. The refrigerant circuit according toclaim 7, wherein the physical quantity is a pressure difference betweenfirst pressure at first position and second pressure at second positionin the refrigerant circuit that is located downstream of the firstposition.
 9. The refrigerant circuit according to claim 8, wherein thedetecting device is provided in the tube, wherein the detecting deviceincluding: a spool that is movable based on the pressure difference; amoving permanent magnet fixed to the spool; and a magnetic forcedetecting device detecting magnetic flux density of the moving permanentmagnet.
 10. The refrigerant circuit according to claim 9, wherein thefirst and the second positions are provided in the tube located betweenthe discharge chamber and the condenser, wherein a throttle is providedbetween the first and the second positions.
 11. The refrigerant circuitaccording to claim 9, wherein a bend is provided between the first andthe second positions.
 12. The refrigerant circuit according to claim 7,wherein the detecting device detects a position of the piston directly.